Embodiments of the invention relate generally to structures of integrated circuits (ICs). More specifically, the disclosure relates to through-semiconductor via (TSV) structures with a metal cap, and methods of fabricating those structures.
TSVs are electrically conductive structures extending through a semiconductor layer or wafer for coupling two or more components on either side of the semiconductor material. In conventional structures, the TSV is substantially perpendicular to a metal layer. This structure may cause electric current to follow a substantially “L” shaped path from the metal layer into the TSV. Typically, current density in this structure is highest at the elbow of the current path.
High current density and local joule heating in one portion of the TSV may cause the TSV to experience electromigration degradation. “Electromigration” refers to physical motion of atoms out of areas where current density is very high. Electromigration is caused primarily by frictional force between metal ions and flowing electrons. Electromigration may damage a metal line or via.
Risk of electromigration can be greatest at a surface of a TSV, where metal contacts a dielectric interface. Over time, electromigration can cause thermal and tensile stresses in portions of semiconductor wiring structures. Thermal and tensile stresses may create “voids.” In general, a “void” is a portion of wiring composed substantially of empty space, and therefore having a high electrical resistance. If voiding occurs, the risk of electromigration damage in the TSV can further increase.